Noise question again

[W2DI]

 
I had a thread on a high noise level in my shack some weeks ago.

After trying some of the great suggestions, I found the source.

In our kitchen, my cable TV/Internet cable comes in and goes to a router. The router is then connected to another router upstairs which goes to one computer.

Also the router in the kitchen, goes to a wireless modem.

When I turn power off to the upstairs BR and the kitchen the S8 noise on 40M drops to 0, or the natural nose floor.

If I have the upstairs router on and and the kitchen off, I get S8. If the kitchen is on and the BR is off I get an S3-4 noise.

Now, I can eliminate the upstairs room router since only one machine is now connected to it. There my be a coupler, but if not, I'll hand wire the cable (It would be impossible to run a new cable.)

So I will have a router, only the in the kitchen, going to the wireless modem - still an S3 noise level.

My question, finally, is what is the best way to get rid of the router/modem noise?

Would wrapping the leads to the wall warts with a choke help? What is the best kind to use?

Thanks very much!!!

joe -- w2di

[VA7CPC]

Finding the problem is 80% of the work -- congratulations!

Wrapping the lead to the wall-wart _might_ help -- it's a cheap, easy solution if it works.  MFJ and Amidon and Palomar all sell clip-on ferrite chokes.  You want the HF ferrite, not the VHF ferrite.  Several turns of the leads through the choke works best.

If the wall-wart is radiating through the house wiring, you might have to replace it with an old-fashioned transformer-based power supply.  Or plug it into an AC line filter, also sold by MFJ.  Or check here (Google is wonderful):

http://www.ky-filters.com/ac.htm

                Charles

[WA3SKN]

OK, you have isolated it to the routers.
Just leave the wall warts connected (no router)... do you still have the noise?  Then connect the router without any cables... do you still have the noise?
This tells you if the power supply is radiating noise.
It tells you if the router is radiating noise through the plastic case.
Now comes the non-shielded CAT 5 cables (think antennas)!
Aluminum foil or screen shielding can be used for the power supply and router... leave some vent holes! (heat).  Ferrites will not be as useful, but can also be used.
Shielding the CAT 5 cables should solve the rest.  Note that the wireless router's RF is in the microwave region and is probably NOT the source for your noise.
Good luck with the project!
73s.

-Mike.

[W2DI]

Thanks Mike and Charles. Good Ideas!!!
I feel I'm getting close.
Thanks again for your expertise.
joe

[K5DVW]

Had a similar problem. I found the noise went away when I disconnected the LAN cable to a certain computer. Somehow the LAN card in that computer spewed out noise only when the cable was connected. So, I got a new LAN card and the problem was solved.

[W2DI]

Thanks Darrin. Gives me another option should other things don't work.
joe

[MM0EEY]

I can confirm the use of shielded cat5 leads will help your problem. I had serious noise issues with my router until I replaced the cables, in fact I try to run as much off the wireless than wired, the 2.4GHz RF shouldn't bother HF.

The wall wart for the router doesn't seem to radiate much but the one for my set top digital TV box was wild. Since been thrown out and replaced with a quieter one.

73

Pete

[W2DI]

Thank you Pete.

Last night, I turned off the router and the noise continued.
I turned it back on and then turned off the wireless modem by unplugging the wall wart from the modem - so the wall wart was still plugged in but not powering the modem. The noise was totally gone.

So I have concluded, rightly or wrongly, that the interference is from the wireless modem only. It is either from the box, or the signal it transmits? But at such a high frequency, the transmitted sig should not bother 40 meters!

The cat-5 cable runs all the way upstairs to a computer and while it was on, and the wireless modem off, the noise was gone. I may have shielded cable already, but I don't know.

So with the assumption that the cable modem box itself is causing the problem, or what it is broadcasting is dirty, does anyone have any other suggestions.

Thanks again to everyone for their time and feedback. I really appreciate it and have learned a lot.

joe -- w2di

[AA4PB]

Have you tried disconnecting all of the CAT5 cables from the modem? This would tell you if the modem is using the CAT5 as an antenna to radiate the noise.

I'm assuming that what you have is a cable modem with several CAT5 connections and wireless antennas. If so, that "modem" is really a cable modem plus a router plus a wireless access point all in one box. What you have upstairs is probably a switch rather than another router.

At any rate, if removing the CAT5 connections eliminates the noise then you have the option of running everything from the wireless access. It may require adding wireless cards to desktop computers that don't presently have wireless access built in. You can be pretty sure that the RFI on HF is not caused by the GHz RF being radiated by the wireless access point. It's probably due to much lower frequency internal digital circuitry or switching regulators and the path out is likely via the CAT5 cables and/or the power connection.

[N3KE]

I'll second the previous suggestion, radiation from CAT5 cables coming out of almost any equipment is a big problem.  It is always the biggest nightmare when passing FCC.

So, try the following:

- Modem plugged into the wall *but nothing else* (either its phone or coax input or any of its CAT5 outputs).  If you've got noise you've either got a P/S problem in the modem or its wireless is radiating something bad.  If you don't have noise then you know it is radiating from a cable.

- Attach the input to the modem (phone or coax).  If the noise now appears you've got a problem on that cable - if it is coax check the shield.

- Attach a CAT5.  If that makes the noise appear then either go fully wireless or get a new modem.  You might try shielded CAT5, but it sounds like you don't have the option to run a new cable.

- If you've had noise regardless of cabling it might be radiating on the wires to the wall wart.  Try some ferrite.  Or it might be the Wi-Fi (even though it shouldn't).  Some modems let you turn off their wi-fi.  If you can access your modem (usually a 192.168.1.1 address) and log in (i.e. your provider hasn't prevented you from doing thing) try disabling the wi-fi.  If that makes the problem go away either get a new modem, or just go get another wi-fi router and connect it to the modem with CAT5.  Of course if something is broken it is possible that an HF source is radiating on the wi-fi antenna even if the wi-fi is off.

Anyway, it sounds like you are getting real close.  Just remember any piece of copper coming out of that thing (including its Wi-Fi antenna) could radiate HF.  The trick is finding which one.

Good luck!  At least it is in your house and not a neighbors!

[W2DI]

Thank you very much Bob and Ken.

I will give it a try tonight.

The actual set-up is something my son did several years ago. The cable comes in the house and goes to the (wire) router. Two machines are connected to the router by cables. There is a connection then to the wireless modem, which serves the other wireless laptops.

With everything turned-on, only turning off the wireless modem will stop the noise...S8 down to the natural noise floor.

So, I will try the cable disconnect routine and see what happens! And hope. Or I may start collecting coins

Thanks again very much.

joe -- w2di

[K8AC]

When I faced a similar problem here years ago, the problem turned out to be radiation from the CAT 5 cables running to my wireless router.  Chokes on those didn't help - replacing them with shielded cables pretty much eliminated my problems.  I bought the cables from one of the online cheap cable places at a fraction of what they cost in a store.

[AA4PB]

Okay, it sounds like you have identified the noise as comming from the wireless access point or its power supply. Disconnect the CAT5 from it and see if the noise is still there. That will tell you if the noise is getting out via the CAT5 or not. The next most likely place to generate noise is the switching mode power supply. Some ferrites *might* help that - on the cable between the supply and the access point.

If its the supply then you might be able to replace it with a linear supply, provided its a single output supply. Purchasing a new wireless access point is another possibility - especially if you can find a store that will let you return it if it generates noise.

[W2DI]

Thanks Floyd and Bob.

You are both on the right track, after my experimenting with things last night.

It was the wireless router itself generating the noise and getting it out, probably via the cables.
Re-running the cables would be difficult, but on the way home I picked up a new router (49.95) and replaced the old one.
Sure enough, 40 meters and the other bands were quiet down to the natural noise floor, save for the normal static crashes, etc!!

The only problem I have now is getting the laptops to recognize the new router...what a mess - but that's another problem to deal with and with my sons and their computer wiz friends, I'm sure we can get that back.

Thanks again to everyone!!! You guys hit it right on the head. This is the best forum I know of and sincerely appreciate everyone's time and expertise.

joe -- w2di